(a) Field
The present invention relates to a secondary battery, and more particularly, to a structure of a safety valve in a secondary battery.
(b) Description of the Related Art
A secondary battery is a rechargeable battery that can be made into a smaller size or a larger size. Common types of secondary batteries include the nickel-hydrogen battery, the lithium battery and the lithium-ion battery. Depending on the external shapes, they may be classified into cylindrical type batteries and square type batteries (e.g., square shaped or rectangular shaped).
Generally, the secondary battery includes a power generating element, that is, an electrode assembly having a positive plate, a negative plate and a separating plate, and a metal container receiving the electrode assembly and electrolyte, and a cap assembly fixed onto the opening of the container to seal the container.
Depending on the structure of the secondary battery, the cap assembly can be made in various forms, one of which has a cap plate welded onto the opening of the container to seal the container, a terminal pin, and a gasket insulating the cap plate from the terminal pin.
The terminal pin is welded onto a negative tap that is drawn out from the negative plate so that the terminal pin functions as a negative terminal.
Furthermore, a positive tap drawn out from the positive plate is electrically connected directly to the bottom of the cap plate or to the inner wall of the container to make the whole outside of the battery except the terminal pin function as a positive terminal.
Meanwhile, a secondary battery has a safety valve in order to prevent the battery from exploding by reducing the internal pressure when gases are generated in the battery and the internal pressure increases to a level higher than a prescribed level.
A conventional safety valve is either formed as an integrated structure of the cap plate or the container through mechanical, etching or electroforming process, or formed as a separate structure attached on the cap plate or the container.
Therefore, conventionally a safety valve must be provided separately to a secondary battery for its safety, and consequently it is necessary to add more process and equipment, which reduces the productivity (increase of complexity of process and manufacturing costs) of a secondary battery.